1. Field of Invention
This invention relates to equipment and a method of decontaminating large volumes of air from any media, e.g. soil, that has been contaminated with mixtures of one or more toxic chlorinated organic solvents and petroleum products by wave energy below 200 nm. More specifically, this invention relates to the equipment and the method related to such chemical decontamination.
2. Description of the Prior Art
There is an urgent need for a portable practical means for the on-site clean up of solvent contaminated soil in situ by various types of low boiling toxic chlorinated organic solvents and/or petroleum products to unwanted non-toxic products. The following is a description of the process, equipment and major problems.
Both above ground and underground storage tanks are used for mixtures of waste chlorinated solvents and petroleum products as well as storage of these individual components. A large majority of these older tanks or their piping connections have leaked into the surrounding soil. Over the years, the soil surrounding the tanks as well as the groundwater have accumulated these materials in high concentrations. In addition, the accidental surface spillage of large volumes of these materials also have contaminated large areas of soil and have permeated into the underground water tables. These conditions represent a hazard to human health. In response to this health hazard, State and Federal Governments have passed laws regulating the clean up and disposal of such contaminated soil and groundwater.
One clean up method requires excavation of the soil and moving it to a truck mounted portable oxidation unit. The unit utilizes an enclosed rotating trommel system to mix an oxidant at room temperature with the contaminated soil. This mixture is then transferred to an enclosed conveyor system with an ultraviolet light source for increasing the reaction rate of the oxidant with the contaminants. This is described in U.S. Pat. No. 4,882,021. The cost of excavation of contaminated soil and the use of an oxidant is expensive. The process cannot be used under buildings encompassing many tens of thousands of tons of contaminated soil.
Another method for the removal of these volatile organic solvents and petroleum products is the use of vapor extraction from the contamination zone using large portable vacuum/blower pumps. In the removal of a mixture of volatile solvents including volatile petroleum products from the permeable soil formation, a high flow rate vacuum/blower pump arrangement is used to draw ambient or heated air at 200-1,000 cfm or higher through the underground formation to extract the organic solvents and/or petroleum products by means of volatilization. The exhaust air from the vacuum/blower pump containing the vapors at 50 to 20,000 ppmv or higher of toxic and hazardous organic solvent and petroleum products is required to be purified before discharge to the atmosphere due to health and safety regulations. This soil vapor extraction process is well known and described in detail in "Petroleum Contaminated Soils", vol 2, by P. T. Kostecki and E. J. Calabrese, editors, chapter 24; and volume 3, chapter 17 (Lewis Publishers, 1989 and 1990).
One attempted solution to the clean up of the chlorinated organic solvent contaminated air before discharge involves the use of ultraviolet wave energy destruction of the chlorinated compounds in the blower exhaust air stream or from water streams. The incoming vapors are adsorbed on a bed of quartz chips or silica gel while irradiating the bed with mercury ultraviolet wave energy in the range of 185-254 nanometers. This is contained in U.S. Pat. Nos. 4,780,287 and 4,941,957. There are limitations to this approach. The mercury wave energy source has only a few weak emission lines below 254 nm and the intensity of these lines is insufficient to destroy high concentrations (&gt;100 ppm) of toxic and hazardous organic solvent vapors in a short period of time. In addition, the ultraviolet energy is reduced considerably in passing through the quartz chip bed to reach the adsorbed solvent vapor molecules. Subsequently, this is limited to low vapor concentrations of &lt;100 ppm and flow rates of &lt;50 cfm. For high incoming toxic and hazardous organic solvent vapor concentrations, e.g. &gt;500 ppm, at flow rates of 300 cfm or higher, a very large packed bed of quartz chips would be required and would not readily allow a portable system.
Another method of removing malodorous or toxic gases from an air stream is contained in U.S. Pat. No. 4,863,687 using ozone, water vapor and ultraviolet wave energy in the range of 210-310 nm. This approach applies to low concentrations of malodorous and toxic gases &lt;100 ppm. It requires the presence of water vapor as one of the reactants. In addition, ozone must be added at levels of 50-200 ppm. This is a disadvantage since it requires a large gas concentration of ozone which is energy intensive and costly to produce. This is not efficient for high vapor concentrations of &gt;100 ppm.
Other approaches to the destruction of the toxic contaminants in an air stream involve using electron beams. U.S. Pat. Nos. 4,882,020 and 4,915,916 both use this method to destroy low concentrations of sulfur or nitrogen oxides either with or without the addition of ammonia at high flow rates. These patents do not address the use of organic solvent vapors or petroleum product vapors in the air stream. A major disadvantage is the use of the electron beam on explosive mixtures of solvents or petroleum product vapors in the air stream.
Another high energy approach for the destruction of waste toxic vapors and gases involves a high frequency electromagnetic wave generated plasma and reactants such as steam, methane, ammonia or acetylene at low concentrations. This is contained in U.S. Pat. No. 4,883,570. One major disadvantage is the potential explosion danger from plasma arcing along the influent pipe to the high incoming concentrations of organic solvents or petroleum product vapors. Another microwave process as shown in U.S. Pat. No. 4,935,114 requires the adsorption of trichloroethylene vapors in an air stream (&lt;1 cfm) onto a charcoal bed doped with a catalyst in a two step process. The charcoal bed is then heated to 400 degrees Centigrade with microwave energy in a flowing air stream. At this temperature, a reaction occurs with the charcoal to produce decomposition gases of trichloroethylene such as hydrogen chloride as well as small amounts of methyl chloride, dichloroethylene and desorbed trichloroethylene vapors. One major disadvantage other than the process is not efficient is that the carbon could burst into flame in the air stream at these elevated temperatures. The process also requires heating for 60 minutes to achieve only 70% destruction of the trichloroethylene.
Thus, the prior art does not yield a satisfactory solution to the problem of ambient temperature rapid destruction of mixtures of high concentrations of one or more toxic and hazardous chlorinated organic solvents and petroleum product vapors in high volume air streams from any media, i.e. soils, in a transportable unit.
The present invention concerns an improved process and equipment for the ambient temperature rapid destruction of mixtures of high concentrations of one or more toxic and hazardous chlorinated organic solvents and petroleum product vapors in contaminated air streams to unwanted non-toxic compounds using ultraviolet wave energy below 200 nm.
This invention can be used for the in situ rapid decontamination of high flow rates of contaminated air arising from large volumes of soil containing toxic and hazardous chlorinated organic solvents and/or petroleum products from underneath buildings and other structures or from any other media other than soil.